An overspeed governor supervising the driving speed of an elevator car is known from patent document DE 36 15 270 C2 (also GB 2,179,795A). The elevator car moves a pulley with an integrated locking rim over a wire rope. A valve timing gear displaces a swing catch with a swing lever in oscillating motions. An operating lever is fixed on the swing lever in a rotational manner, and the operating lever is held in a rest position opposite the swing lever by means of a retaining mechanism. The upper end of the operating lever is formed as an operating bow, at the lower end is located the releasing catch, protuberant opposite a swing catch. Both catches are placed between two locking rim teeth whenever the swivel-join roller stands on a cam. When the swivel-join roller stands between two cams, both catches are raised from the track of the locking rim teeth. In that way, the locking rim teeth passes without acting on the catches. In case of overspeed, the swivel-join roller raises from the valve timing gear. The release catch remains immersed in the locking rim track. A locking rim tooth acts on the release catch and drives out the operating lever. In that way, the operating bow switches off the gear via a switch. With further rise of the car speed, the swing catch dips into the locking rim track and blocks the pulley over the locking rim teeth. The force for the re-lease of a safety gear is developed through the friction in the rope groove.
A disadvantage of such a known mechanism lies in the fact that the stopping of the elevator car can also take place if no necessity exists.